The present invention is directed to gaseous discharge lamps. More particularly, the invention is directed to resistively ballasted gaseous discharge lamp operating circuits and methods of operation.
A gaseous discharge lamp, e.g., a metal halide gaseous discharge lamp, may be characterized as having three modes of operation, i.e., an initial high voltage breakdown mode, a glow-to-arc transition mode, and a steady state run mode. The typical circuit operating the lamp provides about 2-4 kilovolts to achieve initial breakdown in the lamp and then sufficient xe2x80x9copen circuit voltagexe2x80x9d (OCV) to effect a glow-to-arc transition in the lamp and stabilize the lamp in a steady state run mode.
Metal halide gaseous discharge lamps are typically constructed to run from direct current (DC) in order to give more consistent light and color rendition. To operate such lamps from standard 120 volt alternating current (AC) power sources it is necessary to rectify the AC power source to supply direct current to the lamp. The lamps are typically designed to operate at a certain fixed voltage across the lamp terminals and are biased to operate at a specific wattage by controlling the current that passes through the lamp. Gaseous-discharge lamp circuits must include a means for limiting the current through the lamp.
Some conventional circuits use an ordinary resistor to limit the current through the lamp. Other circuits include an incandescent lamp filament to provide resistance. In such circuits, the resistance of the lamp filament increases as the current through the lamp increases, thereby opposing the increase in current through the lamp. As a result, the resistive lamp filament maintains the overall current through the lamp approximately constant. The characteristics of the current limiting filament lamp are selected to provide the proper operating current for the arc discharge lamp.
The basic lamp running circuit includes a DC arc discharge lamp connected in series with an incandescent filament lamp. The arc discharge lamp is powered by DC provided to the lamp by rectifying the standard 120 volt AC supplied to the circuit from the AC power source. In addition to meeting the specifications for running the lamp in the steady state run mode, the lamp operating circuit must also provide for the other two transient modes of operation (i.e. the initial high voltage breakdown mode and the glow-to-arc transition mode).
The voltage obtained by using a typical full-wave bridge-rectifier configuration and a capacitor or storage filter operating from 120 volt AC is sufficient to operate the lamp in the steady state run mode. However, the rectified voltage is less than the OCV required to effect a glow-to-arc transistion in the lamp. Therefore, the rectified voltage (i.e., the DC line voltage) must be temporarily boosted during lamp startup to effect the glow-to-arc transition. Once the lamp is in the run mode, the lamp develops a terminal voltage that is less than the DC line voltage. Thus a current limiting means, such as an incandescent lamp filament, is placed in series with the rectified power source and the gaseous discharge lamp to maintain the lamp in a steady state run mode at the terminal voltage of the lamp.
The OCV required to effect the glow-to-arc transition in the lamp may be provided by a voltage doubler. Conventional DC lamp operating circuits include voltage doublers to boost the voltage during the lamp starting process. However, in these operating circuits the voltage doubler remains in operation during the steady state run mode of the lamp resulting in wasted energy, i.e. excess energy must be dissipated in the filament lamp during the run mode. In addition, conventional voltage doublers are by necessity xe2x80x9chalf-wavexe2x80x9d and, therefore, require a larger filter capacitor to eliminate the xe2x80x9cripplexe2x80x9d effects which cause lamp flicker.
Many prior art lamp operating circuits include complex electronic circuits to control the lamp current. This type of electronic ballast provides greater efficiency than ballasts including a lamp filament as a current limiter. However, this type of electronic ballast typically includes several high-frequency magnetic components in the form of inductors, transformers and other ferrite-core devices. As a result, the electronic ballast is expensive and also generates electromagnetic interference requiring the use of filters to meet FCC standards.
A filament ballast is less complex and thus less expensive than an electronic ballast. A filament ballasted lighting unit may be produced for about ten percent of the cost of a comparable unit with an electronic ballast. The filament ballasted lamp produces negligible electromagnetic interference (EMI) during the run mode, and only a minimal amount of interference during lamp startup. As a result, there is no need to use EMI filters.
However, the economy of a filament ballasted lamp may be further improved by simplifying the circuit and making multiple use of components to improve the overall efficiency of the filament ballasted lamp circuit.
Accordingly, it is an object of the present invention to provide a novel and improved gaseous discharge lamp operating circuit and method.
It is another object of the present invention to provide a novel arc discharge lamp operating circuit and method including a current-limiting lamp filament.
It is still another object of the present invention to provide a novel arc discharge lamp operating circuit and method for doubling the voltage of the DC line voltage to effect an arc condition in the lamp.
It is yet another object of the present invention to provide novel arc discharge lamp operating circuits and methods for providing immediate light during startup of the lamp.
It is another object of the present invention to provide a novel arc discharge lamp operating circuit and method wherein an incandescent lamp filament is illuminated only during a half-cycle of the AC power source during startup of the arc lamp.
It is another object of the present invention to provide a novel arc discharge lamp operating circuit and method for doubling the DC line voltage of the circuit and isolating a rectifier bridge storage capacitor from the DC voltage applied to the lamp to establish an arc condition during lamp startup.
It is yet a further object of the present invention to provide a novel method of operating an arc discharge lamp circuit with a bridge rectifier and storage capacitor that includes isolating the storage capacitor from the voltage required to cause the lamp to pass through the glow-to-arc transition mode.
It is a further object of the present invention to provide a novel circuit and method for operating an arc discharge lamp powered by a three phase AC power source that eliminates the need for a storage capacitor.
It is still a further object of the present invention to provide a novel method of operating an arc discharge lamp by resistively ballasting the lamp during the steady state mode with an incandescent lamp filament which also illuminates during startup of the arc discharge lamp.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.